A gas insulated device used for power distribution purposes in an electric power substation, such as a gas insulated switchgear, a gas insulated circuit breaker, or gas insulated bus bar, has a grounded sealed metal container in which a high-voltage conductor is accommodated. Further, the sealed metal container is filled with an inert insulating gas such as SF6 and is thereby insulated. With this construction, the insulation performance is improved, and thereby the size of the electrical device can be reduced and safety thereof can be improved as compared to a conventional air insulated or oil insulated electrical device.
When a contact failure or incorporation of metal foreign matters occurs in the grounded metal container of the gas insulated device, the insulation performance is degraded at that portion, which may result in occurrence of partial discharge. If this partial discharge is left untreated, a breakdown occurs, which may lead to a serious accident.
In order to prevent occurrence of such a serious accident, it is necessary to detect and deal with the degradation in insulation performance in the grounded metal container in the early stage. Under such circumstances, an insulation diagnosis technique such as a partial discharge detector for detecting the partial discharge caused by the degradation in insulation performance is now under development.
Recently, from the point of view of achievement of long-term and stable operation of the device, so-called a UHF method has been used as an external diagnosis method for performing status monitoring. The UHF method is a method for measuring an UHF-band (0.3 to 3 GHz) partial discharge signal and is now ready for standardization by the IEC (International Electrotechnical Commission).
Generally, in the UHF method, an electrode (antenna) provided in the grounded metal container is used to detect a high-frequency electromagnetic wave induced by the partial discharge. The insulation diagnosis can be achieved by detecting the partial discharge at this time. Such an electrode for partial discharge detection is an electrode for detecting a high-frequency electromagnetic wave, so that two electrodes, i.e., a detection electrode and a ground side electrode, are required.
These electrodes are arranged so as to be electrically insulated from each other. There is known a method as disclosed in Japanese Patent Application Laid-Open Publication No. 2001-141773, the entire content of which is incorporated herein by reference, in which the shapes of the two electrodes and arrangement thereof are modified to improve the detection performance of the two electrodes.
Further, as disclosed in Japanese Patent Application Laid-Open Publication No. 63-056112, the entire content of which is incorporated herein by reference, there has conventionally been known an insulation diagnosis method in which an internal shield buried in an insulating spacer is used as an antenna for partial discharge detection to detect the partial discharge in a state where a measurement voltage is decreased by inserting a resistor between the internal shield and a measurement unit.
A common type gas insulated device disclosed in Japanese Patent Application Laid-Open Publication No. 63-056112 is constituted by a high-voltage conductor, a grounded metal container including the high-voltage conductor inserted thereinto and encapsulating an insulating gas such as SF6 gas, and an insulating spacer supporting the high-voltage conductor. The insulating spacer includes a spacer main body and a metal flange formed at the outer periphery of the spacer main body. The spacer main body includes an insulating portion. A high-voltage side internal electrode and a ground side internal shield are integrally formed in a buried manner in the insulating portion.
A female screw portion is formed in the metal flange. The female screw portion is fixed to the metal flange formed in the grounded metal container by fastening means such as bolts.
The metal flange is integrally fixed by a metal member to the spacer main body. That is, the spacer main body and the metal flange have different structures from each other. At least four depressed portions are formed in the outer peripheral potion of the spacer main body and the inner peripheral portion of the metal flange. The metal member is fitted in the depressed portions.
These depressed portions and metal member are formed so as to hold the spacer main body and metal flange in the axial and radial directions of the insulating spacer. Further, the metal member is fastened and fixed to the metal flange by bolts.
The potential of the internal shield buried in the spacer main body is maintained by connecting the internal shield a bar attached to the metal member. Further, a contact metal material electrically connected to the bar protruded from the internal shield is provided in the metal flange. A resistor element and the like are arranged inside the contact metal material.
A voltage divided by a resistance value of the resistor element is detected by a partial discharge measurement device as a partial discharge signal.
However, the conventional gas insulated device has the following technical problems.
The partial discharge detection unit uses the internal shield that is buried in the spacer main body of the insulating spacer that supports the high-voltage conductor as an antenna for detecting a high-frequency signal induced by the partial discharge. That is, a high-frequency signal propagating in the grounded metal container is detected by the internal shield inside the insulating spacer. In this method, the resistor element is inserted between the internal shield and measurement unit to decrease the measurement voltage for detection of the high-frequency signal.
However, in such a signal detection method, not only a UHF-band electromagnetic wave induced by the partial discharge but also, e.g., an inductive component of a commercial power frequency voltage flowing through the high-voltage conductor is detected. The resistance value of the resistor element is generally set with the detection of a commercial power frequency as a premise, so that if a high voltage, such as switching surge, caused at the time of opening/closing an disconnector is applied, the resistor element may be damaged.
The resistor element is designed with detection of a frequency of kHz order in mind. Thus, a plate is attached to a spring constituting the resistor element so as to make influence of the inductance negligible. Further, an insulating cylinder or the like is provided for the purpose of taking out the divided measurement voltage. Accordingly, the structure may become complicated.
That is, the conventional partial discharge detection unit using the internal shield has both a function of detecting a commercial power voltage having a comparatively low frequency and a function of detecting the partial discharge. Therefore, even in the case where only the partial discharge is required to be detected, the commercial power voltage is also detected at the same time, making it difficult to achieve effective detection of the partial discharge.
Generally, in the gas insulated device, a plurality of grounded metal containers are coupled to constitute a complicated pipe arrangement in order to meet various installation conditions such as an installation space condition. The gas insulated device includes a plurality of insulating spacers between adjacent grounded metal containers.
It is desirable that the gas insulated device having the plurality of grounded metal containers includes a plurality of partial discharge detection functions aimed at abnormality detection in order to make it easy to identify the location of abnormality. Thus, when a function for detecting the partial discharge is provided for each insulating spacer arranged between the adjacent grounded metal containers, it is possible to achieve partial discharge detection at a plurality of locations without newly providing a detection section.
However, it is not necessary that the commercial power voltage detection function is imparted to all the insulating spacer, and it is sufficient for the commercial power voltage detection function to be provided at one location. Therefore, the commercial power voltage detection function may be provided separately from the spacer.